Fluorescence readers are often used for re-sequencing or gene expression studies. In these systems, light such as that from a laser is directed onto a target, which may include molecules capable of fluorescing. Of course, the light could come from the process of chemi-luminescence as well. The emitted fluorescent light is then detected and analyzed. Oftentimes, multiple color dyes are utilized. For example, four colors may be used. The light is detected by florescence detection devices such as confocal scanning microscopes and imagers that utilize detection elements such as photomultiplier tubes (PMTs), avalanche photo-diodes (APDs), and charge-coupled devices (CCDs).
The data obtained from fluorescent readers are subject to certain forms of error. For example, unintended sources of electromagnetic radiation (e.g., sources of radiation other than the fluorescent molecules on the target) may emit light that is received by the reader, and interpreted as having originated from the target. Additionally, the reader may include automatic gain control circuitry that improperly amplifies or attenuates the received signal, based upon the intensity of emitted light from regions of the target having been read during a previous period of time. Either source of error causes the reader to associate a given region of the target with an erroneously high or low radiation intensity value. Other sources of errors exist, and these sources of errors also reduce the reliability of the information developed by the reader. Such other sources of error include, without limitation, autofocus error that places the focal plane differently for right-going and left-going scans, and mechanical torque of the optical components during motion, which tends to change the optical gain depending on the scan direction.
Typically, a fluorescent reader scans a surface of the target on a line-by-line basis, proceeding either left-to-right or right-to-left while scanning a given line. (Of course, the reader may scan the surface on a line-by-line basis, proceeding up-to-down, or down-to-up, or in any generally linear direction. Usually, the linear direction is chosen so as to permit relatively fast scanning). It has been observed that some sources of error exhibit a correlation to the direction in which the scanning occurs. Accordingly, some scanning techniques have been developed to reduce errors related to direction of scan (some of these techniques also reduce the Gaussian noise exhibited in the received signal). Unfortunately, these techniques may be slow under certain circumstances.
As suggested by the foregoing, there exists an opportunity for an improved scanning technique. Such an improved scanning technique may reduce sources of error related to direction of scan, may be performed relatively quickly, and may be relatively inexpensive.